Regarding a wide frequency bandwidth trunked radio communication system, an analog trunking system using a control channel and a telephone communication channel has been described in Japanese Patent No. 2724917 specification 1. In the analog trunking system according to this Patent Document, when all telephone communication channels are busy, a control channel for communicating control signals is used as a telephone communication channel, whereby all wireless relay channels are assigned as telephone communication channels. However, the above analog trunking system of the Patent Document has the following problems.
Specifically, when all telephone communication channels are busy, a control channel is used as a telephone communication channel, and thus a state where there exists no control channel temporarily occurs. In such state, a wireless unit accommodated by a wireless relay having a control channel cannot await a control signal. Accordingly, the wireless unit will frequently perform scanning operation, thus increasing current consumption.
A further problem is that when a control channel is switched to a telephone communication channel, in the site using the channel, the trunk operation cannot be performed until the telephone communication by the above channel is completed.
An object of the present invention is to make switching between control channel and telephone communication channel more efficient and to reduce current consumption in a wireless unit and at the same time to reduce the time period for which the trunk operation is inoperative.